THE GROUND LAYER Except where it is clothed with plants, the ground layer and its intricate living processes are often overlooked in gardening circles, yet the events that occur here are among the most important to life in the entire ecosystem. The forest floor is where accumulated organic material is decomposed and made available once again for plant nutrition by a myriad of fungi and bacteria, earthworms, insects and other arthropods, and mammals. It's unfortunate that the term most often used for the accumulation of organic matter on the ground is litter, because this material is anything but trash. Dictionaries typically define litter as “trash or garbage lying scattered about” or as an “untidy accumulation of objects.” The general connotations of worthlessness and messiness obscure the essential nature of this material, and the beauty inherent in the process of organic recycling. Ground layer litter, in the form of leaves, twigs, bits of bark and dead wood, seeds and seed pods and capsules, plays critical roles in conserving moisture, replenishing nutrients, and creating niches—microhabitats—needed by various species of animals and plants especially in their earliest stages of regeneration. Duff is an alternative term referring to dead plant material that that has accumulated on the ground. The profile of typical upland woodland soils consists of vertically arranged horizons grading into one another but distinguished by individual letter names assigned by soil scientists. The uppermost horizon, called O for organic, hasan Top Seedlings of dwarf ginseng ABOVE Freshly fallen leaves of blackoe ? : (Panax trifolius) benefit from nutrients |§ gum (Nyssasylvatica) add color to the upper zone containing still-recognizable dead recycled from decomposing organic ground layer of a West Virginia woods plant and animal matter and a lower zone of matter in a Pennsylvania woods in October. Bacteria, fungi, and minute unrecognizable decomposed matter (humus). in mid-April. Fallen branches and pocomposers including springtails other bits of wood act as reservoirs break down the leaves’ organic matter, Below this, the A horizon, or topsoil, has high for rainfall and provide moist shady creating nutrient-rich humus. mineral content but also incorporates signif- niches ideal for germinating seedlings. icant organic matter including humus which gives it a typically dark color. The subsoil, or B horizon below, has relatively little organic The GroundLayer 47
ABOVE Unlike bacteria, fungi are capable of breaking down the high lignin content in wood. RIGHT A mossy patch onthe ground layer of a woodland in Pennsylvania’s Pocono mountain region in October. Because they have no vascular system for transporting water internally, mosses typically inhabit shady moist niches that minimize the risk of desiccation. They often establish themselves where the humus-rich ground layer is exposed to filtered sunlight, in turn providing ideal conditions for germinating seedlings of vascular plants such as the wintergreen (Gaultheria procumbens) in this photo. matter and a generally lighter color. Below it, the C horizon consists primarily of partially broken down rock, and below that is the bedrock, known as the R horizon. Specialized soils may contain additional horizons, and disturbed soils may have missing horizons or the horizons present may be partly inverted. If mosses, fungi, algae, insects, arthropods, and related macroinvertebrates are counted, the ground layer including the O and A horizons support more species diversity than any other woodland layer. Many long-evoived relationships are evident between plant and animal life in the ground layer and associated layers. One of the more interesting examples is the interaction between many early spring wildflowers and
ants. Bloodroot, trillium, Dutchman’s-breeches, squirrel-corn, and trout lily are among the species that depend upon ants to help with seed dispersal. Their seeds have a nutritious appendage (elaiosome), which is not necessary to the development of the seedling but is valued by ants. Ants carry the seeds back to their nest, snip off the elaiosomes with their mandibles, and feed them to their larvae. The seed itself is of no value to the ants so they dispose of it in a waste area within the nest, which happens to be an ideal place for the seed to germinate and grow intoa new plant. This mutually beneficial interaction (mutualism) helps sustain ant larvae while providing low-growing spring wildflowers with a means of widely dispersing their seeds. RIGHT So tiny that they usually go unnoticed, springtails are essential to the decomposition of organic matter in the ground layer. Typically only 2 millimeters long, springtails are macroinvertebrates that were once grouped with insects but are now classified separately. Among the most abundant of modern macroscopic animals, springtails are part of a lineage that can be traced back to the Devonian period approximately 400 million years ago. ABOVE RIGHT A flat millipede (Apheloria virginiensis) makes its way through the ground layer of a Virginia woodland in May. Millipedes are important decomposers of organic matter and, along with earthworms, they play roles in working soils and creating favorable conditions for essential soil bacteria. LEFT AND BELOW Bloodroot (Sanguinaria canadensis) is one of many spring ephemerals that depend upon a mutually beneficial relationship with ants for seed dispersal. The smooth green capsules of bloodroot contain multiple seeds, each with an elaiosome. The second image shows an ant carrying a bloodroot seed back to its nest. The elaiosome is the transparent appendage attached to the redbrown seed. FAR LEFT Land Snails are terrestrial mollusks that eat low-growing leaves, stems, fruit, algae, and fungi. They are most common in areas where soil calcium is abundant because they requirea great deal of calcium to make their shells. Land snail shells, in turn, are an important source of calcium for many breeding birds when they are making their calcium-rich eggshells. LEFT Salamanders, like many other inhabitants of the forest floor, require environments with consistently high humidity. Most salamander species exchange gases through their skin and this form of “breathing” requires moisture to be effective. Salamanders are active primarily at night when humidity is high and there is no exposure to the drying effects of sunlight. They thrive in habitats where abundant leaf litter and woody debris enable them to hide from predators while remaining within an envelope of moisture near the ground. The GroundLayer 49
ABOVE Chipmunks and other small mammals unwittingly aid in the dispersal of acorns and other seeds since they often fail to eat all the acorns they stash in hiding places, especially in years when acorns are abundant. BELOW While they are decomposing, fallen logs contribute to life just above the ground layer by serving as moisture reservoirs and as shelter and storage sites. What may have once been a woodpecker hole in this chestnut oak log has been filled with acorns by a chipmunk, a squirrel, or some other small mammal. RIGHT In January ina Delaware woodland, a fallen tree provides a perch for a Carolina wren, which is dividing its time between scouting its territory and foraging in the leafy ground layer. The wren’s colors closely match the ground layer, making it difficult for predators to spot as long as it stays still.
Pileated woodpeckers, one of North America’s most charismatic birds, use all layers of wooded landscapes in their daily routine. Like most woodpeckers, pileateds use their beak to drill into soft wood for larvae of wood-boring beetles. This type of food is rich in protein and lipids but is hard to find, so pileateds must forage long hours each day in woody substrates from the top of the canopy to fallen logs on the ground. Carpenter ants are even more desirable than beetle larvae. When a woodpecker senses a carpenter ant nest within a tree, it excavates as much of the nest as possible by pounding out large rectangular holes deep enough to reach the heartwood where the carpenter ants live. A large ant nest may require several excavations, usually stacked one ontop of the other, to reach all of its occupants. Such rectangular tree cavities are the hallmark of pileated woodpeckers, as no other woodpeckers create holes of this size or shape. Pileateds nest and roost in natural tree cavities such as the beech holes in the images below, but more often they create their own cavities high in the canopy. Nesting high reduces the chances that raccoons, opossums, or black, gray, and yellow rat snakes will find and eat the nestlings. Pileated woodpeckers are so-called indicator species: their presence ina forest is an excellent indication that it is a mature and functioning ecosystem.
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THE DYNAMIC EDGE If we leave the woodland’s vertical layers and begin an exploration of lateral layers, the first zone that becomes apparent is the edge. In ecological terms, edge is a local transitional zone where two different habitats or ecosystems meet. The edge can also be recognized as a habitat in itself comprised of a dynamic mix of biotic (living) and abiotic (non-living) elements from two adjacent habitats. Depending upon how different the habitats are, the edge may be readily apparent or quite subtle. In temperate North America, the transition from woodland interior to wetland, meadow, or grassland is among the most dramatic and most ecologically dynamic of all. The visual drama is due to the startling difference in illumination and structure: from shade to sun and from stately enclosure to expansive openness. The ecological dynamism is the result of enhanced opportunities provided by the concentration and juxtaposition of diverse environmental resources. Similar in meaning to edge is the term ecotone, which ecologists use to refer to a transitional zone between adjacent ecological systems. Ecotone may be used to define a local transition but is often used to refer to transitions on a grand scale, such as the transition from the deciduous forest biome of eastern North America to the freshwater aquatic biome of the coast, or to LEFT A sourwood (Oxydendrum arboreum) thrives in conditions at the edge of a West Virginia mountain woodland in mid-October. As is the case with so many edges in the modern landscape, this landscape is the result of clearing and re-grading for a transportation corridor. RIGHT Backed by the bright yellow of a sassafras, a flowering dogwood growing along a sunny edge produces a heavy berry crop. Though Cornus florida can tolerate the low light in the understory of woodland interiors, it is less affected by the dogwood anthracnose disease (Discula destructiva) when growing at edges and in other more exposed habitats. the grassland biome of the central and western regions. Edges and ecotones typically exhibit a high degree of flux: a constantly shifting flow of resources and organisms. They are often characterized by relatively high biological diversity; however, an excessive edge component created by disturbance can result in dramatically reduced diversity, especially in specialist species. Edges are frequently encountered features of most landscapes, but they are a defining element of suburban residential landscapes. Increased flowering, seed production, and intensified autumn coloration are among the most obvious effects of increased available sunlight in edge habitats as the following photos illustrate. Even the form of trees may be affected as they stretch toward the sunlight. Yet another benefit of increased available sunlight in edge habitats is better health for the plants growing there. More sunlight means increased air circulation, which minimizes the amount of time leaves and flowers remain moist from rain or dew, and thus inhibits growth of fungus on plants. The Dynamic Edge 53
TOP LEFT Shadbush (Amelanchier arborea), sassafras (Sassafras albidum), and various oaks bloom profusely while maples (Acer species) are already developing their bright red samaras along a woodland edge in northern Delaware in mid-May. LEFT The tiered branching structure of blackgums (Nyssa sylvatica) becomes even more pronounced in trees growing toward sunlight along this edge in western Pennsylvania. The blackgums share the edge with chestnut oaks (Quercus montana) and sweet birches (Betula lenta), and, in the shrub layer, witch hazel (Hamamelis virginiana) and great laurel (Rhododendron maximum). ABOVE Spring iris (Iris verna) easily pushes up through leaf cover on the ground layer of a Virginia forest, taking advantage of increased sunlight near the edge. LEFT Flame azaleas (Rhododendron calendulaceum) are common throughout this Virginia deciduous forest, but the only ones blooming are at the woods’ outer edges or at interior edges below canopy Openings caused by storms or fallen trees. BELOW A Baltimore oriole feeds its young in the distinctive pouched nest that is typical of the species, built here ina sycamore (Platanus occidentalis) at the edge of woods. The Baltimore oriole is an example of an avian species that is adapted to edge habitats but also relies on adjacent forests or woodlots for foraging. The Dynamic Edge 55
individuals can core tasks that would. challenge — the most capable gardener?
ABOVE Redbuds and New Jersey tea (Ceanothus americanus) are among the pioneer species along anew sunny edge in West Virginia. New Jersey tea can withstand considerable drought but is not tolerant of the low light in woodland interiors. LEFT Named for its curly seed structures, curly-heads (Clematis albicoma) is aclump-forming member of a genus characterized by vining species. This early May photo in Virginia illustrates its ability to self-sow and thrive in very dry conditions ona shale-covered slope at the edge of an oak-maple woodland. The extensive root systems of plants established from seed onsite are the key to survival. The Dynamic Edge
= aS eR. se . kt. aS 0y-4IE Se eee Pring feagee ey ee a 9g A, AS 3 dgehabitatin __ > interiorsmay = = = result from canopy openings dueto x nen "storms but is also “<=. common along Fae ay ® . ~ ee” - « » Streams and creeks~ ~ > fae - runhing through a ie “woodlands, as = Es ae — - » (=~ illustrated by this ~~ Na -- early May photo of “-" arocky watercourse { inVirginia. ~ R \ Bb Sy
WET EDGES Some of the most productive, biologically diverse habitats are edges where woodlands meet consistently moist ground or wetlands. This most commonly occurs when a stream or creek runs through the woods, suppressing tree growth and creating a linear opening in the canopy, or at an interface where tree growth is rather abruptly stopped by constantly wet conditions or deep water. The latter type of edge is typically created by rivers, lakes, or ponds. Vegetated edges reduce erosion and help reduce water temperatures in summer, contributing to the health of the habitat. Plants arrange themselves in response toa moisture gradient combined with changes in available sunlight. ABOVE Tiger swallowtails “puddle” at the wet woodland edge. The purpose of this puddling behavior is to obtain essential salts and amino acids. Droppings of wading birds and other animals foraging along the edges of streams and creeks provide concentrations of salts, which often attract butterflies. LEFT Wet edge habitats along ponds, creeks, streams, and other watercourses are essential for many wading birds including great blue herons, which make use of elevated perches including rocks, tree stumps, and fallen branches during scouting and foraging activities. WetEdges 59
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OPPOSITE TOP Sweet pepperbush (Clethra alnifolia) turns bright yellow at the end of October in a wooded edge along a slow-moving stream in southern New Jersey. The mix in this edge includes highbush blueberry (Vaccinium corymbosum), turning bright crimson, and Atlantic white cedar (Chamaecyparis thyoides). FAR LEFT In late October, Virginia sweetspire (Itea virginica) stretches out from a wet edge along a pond in southern New Jersey. Like many other species that only occur in wet edge habitats, Itea is capable of growing in drier conditions. LEFT An adult praying mantis waits for prey on a stalk of Itea virginica. ABOVE In this edge in the New Jersey Pine Barrens, the open water in the foreground supports fragrant waterlilies (Nymphaea odorata). As the water becomes more shallow, smooth rush (Juncus effusus) becomes dominant. Further back on slightly higher ground where the soil is wet or moist but there is no standing water, highbush blueberry (Vaccinium corymbosum) creates a virtual hedge of crimson. At the rear, on high dry ground, pitch pines (Pinus rigida) and scrub oaks including Quercus marilandica dominate. Wet Edges 61
LEFT Amale ebony jewelwing (Calopteryx maculata) rests ona branch leaning out from a wet edge on Ferncliff Peninsula in western Pennsylvania. One of eastern North America’s most distinctive damselflies, it lives only near wooded streams and rivers. Many other plants and animals thrive along this same stretch of wet woodland edge. ABOVE Thecomposition of plants and rock in this section of the Ferncliff edge appears gardenlike but it is completely uncontrived. The two foreground shrubs, sweet azalea (Rhododendron arborescens) and smooth alder (Alnus serrulata), are backed by a mass of great laurel (Rhododendron maximum).
top Perhaps easily overlooked in summer, royal fern (Osmunda regalis) is a dramatic presence in mid-October along the Ferncliff edge, here mixed with smooth alder (Alnus serrulata). ABOVE The sweetly scented flowers of Rhododendron arborescens appear in June. Other shrubs adapted to this wet edge include May-blooming ninebark (Physocarpus opulifolius) and July-blooming buttonbush (Cephalanthus occidentalis), which is providing nectar to a silver spotted skipper (Epargyreus clarus). * Black swallowtails take nectar froma variety of herbaceous species growing along the Ferncliff edge including Turk’'s cap lily (Lilium superbum). Wet Edges
WETLANDS Extensive wetlands and truly aquatic environments are uncommon in residential landscapes, and for this reason they are not covered in this book. However, since many residential landscapes do include patches of constantly wet ground, and these are most appropriately populated with wetland species, it is worth looking at a few of the plant associations representative of such habitats. Although wetlands, swamps (a wetland populated by both herbaceous and woody vegetation), and marshes have long been judged worthless and the typical approach has been to drain them, their importance to the health of regional waters and wildlife is now understood and they are being conserved. The majority of plants that occur in wetland habitats have root systems that are tolerant of saturated soils and low aeration. This gives them a competitive advantage in wet and moist habitats; however, many are adaptable to moisture levels and soil conditions common in suburban residential landscapes. Swamp rose-mallow (Hibiscus moscheutos) often grows with other species adapted to sunny wet conditions including buttonbush (Cephalanthus occidentalis), cardinal flower (Lobelia cardinalis), and blue vervain (Verbena hastata). This adaptable species is easily grown in garden soils of average moisture. Redstem or red osier dogwood (Cornus sericea) is another shrub that is tolerant of periodic standing water. It is stoloniferous and can grow to form large colonies. Winterberry (Ilex verticillata) often tolerates standing water for considerable periods. SSS : a a] . ; OPPOSITE Swamp rose-mallow (Hibiscus moscheutos) blooms in mid-Augustina sunny wetland in northern Delaware. BELOW This early spring image shows redstem dogwood (Cornus sericea) dominating the shrub layer in a wet, open deciduous woodlands in Michigan. i i 4 A a 4 Wetlands 65
RIGHT A painted turtle peers through a haze of jewelweed (Impatiens capensis) at the edge of a tiny Maryland pond, trying to spot the photographer. The log is an important part of the turtle’s habitat. FAR RIGHT Winterberry (Ilex verticillata) is adaptable to a wide range of moisture conditions but occurs naturally only in wet habitats. BELOW Winterberry forms the shrub layer of an open wet woods in western Pennsylvania. — t £ 4s 4 i ANS, a aw ae) = 66 Layers in Wild Landsc
ABOVE This open community of red maples topping an herbaceous layer of skunk cabbage (Symplocarpus foetidus), tussock sedge (Carex stricta), and cinnamon fern (Osmunda cinnamomea) qualifies as aswamp. The structure, form, pattern and luminous qualities of this landscape are especially appealing late ona spring day when illuminated by slanting sunlight. ABOVE New fronds of cinnamon ferns emerge among skunk cabbage foliage in early May. These two species are well balanced and can live side by side for decades. ABOVE RIGHT Spring peepers (Pseudacris crucifer) are amphibians that need the aquatic conditions found in swamps, marshes, ponds, or ephemeral wetlands to support their early egg and tadpole stages. The adults are carnivores that are most active at night, when they emerge from hiding places in the vegetation to feed on insects and other small invertebrates. Only male frogs have the expandable vocal sac required to make the species’ distinctively loud, high-pitched peep. Spring peepers typically begin breeding at dusk and often continue into morning. Their mating chorus can carry for a mile or more through the night landscape. Wetlands 67
MEADOWS AND GRASSLANDS In North America east of the Mississippi River, meadows and grasslands have two things in common: they are frequently encountered and yet they rarely occur except as the result of human activity, past or present. The soils and climate in this region are generally ideal for woody plants, and asa result, forests are the dominant vegetation. Excluding places where forests have been removed by humans, meadows occur here only in places where consistently high moisture discourages woody growth. Similarly, though grasslands dominate the Prairie region to the west, they occur here only in places frequented by wildfires, along coastal areas with high salt concentrations, or in places where extremes of moisture or soil chemistry are unsupportive of woody growth. Examples are serpentine barrens, with their high-magnesium and low-nutrient levels, pine barrens, which are classic fire ecologies, and coastal sand dunes. The vast majority of meadows and grasslands encountered within the expanse of rural, urban, and suburban landscapes where most of us live are the direct result of deliberate clearing for agriculture or other industry. Since the activities that motivated these clearings have often ceased or are waning, most meadows and grassy places in this region are transitional: they are highly dynamic habitats that are essentially ephemeral. Without intervention, woody vegetation eventually regenerates and becomes dominant. In the meantime, these often beautiful, unstable systems typically support high floral and faunal diversity. LEFT Sweeps of ironweed naturally occurring only (Vernonia noveboracensis) if the definition of natural and boneset (Eupatorium includes human activity. perfoliatum) mix with gold- Once forested, this land enrods (Solidago species) was cleared long ago for and grasses in a moist pasturing. The ironweed's western Pennsylvania heavy presence today is in meadow in late August. part because long-gone Such meadows are Spontaneous meadows like this upstate New York example often provide opportunities for the local native flora. maculatum, a Joe-PyeIn this early September weed species more view, the meadow is frequently encountered enlivened by Eupatorium __innorthern states. cows found it unpalatable and avoided it. ABOVE lronweedisa popular nectar source for many lepidopterans including tiger and black swallowtails. Meadows andGrasslands 69
ABOVE Cutleaf coneflowers (Rudbeckia laciniata) and ironweed (Vernonia noveboracensis) are responsible for the late August show in this eastern Pennsylvania floodplain meadow. In background, sycamores (Platanus occidentalis) and black willows (Salix nigra) follow the course of the adjacent White Clay Creek. Continual regeneration of this community depends upon periodic flooding plus maturation and dispersal of the yearly seed crop of these colorful forbs. LEFT Intransition from its former role asa small pasture, this self-seeded meadow in northern Maryland owes its early September color to goldenrods (Solidago species), roundleaf thoroughwort (Eupatorium rotundifolium), and slender false foxglove (Agalinis tenuifolia), a locally native annual species.
ABOVE LEFT Maximilian sunflowers (Helianthus maximiliani) mix with bushy beardgrass (Andropogon glomeratus) in an east Texas farm pasture turned to spontaneous meadow, with a large burr oak (Quercus macrocarpa) in background. Though moist, the moisture is insufficient to discourage woody growth, andina few years, this meadow will again become woodland unless woody plants are selectively removed. aBove A black swallowtail takes nectar from Maximilian sunflower. Though this meadow was once forested, —_ of most of the trees while creating something has changed and the area is ideal conditions for golden ragwort now frequently inundated. The newly (Senecio aureus), which is thriving in wet conditions have caused the death the increased sun and moisture. Meadows andGrasslands 71
ABOVE The capacity of switchgrass (Panicum virgatum) to tolerate low-nutrient soils and moisture conditions that annually run from extremely dry to waterlogged allow it to out-compete most other species on this sandy slope edging a slow-moving stream in the New Jersey Pine Barrens, creating a localized grassland within the forest. LEFT The dry, low-nutrient conditions of this sloped ground on a former farmstead in upstate New York have resulted ina self-sown near-monoculture of locally native little bluestem (Schizachyrium scoparium).
PIDRC IAI CVCRY 1 RI Mc IAL EVE 1 (/EeD DIRDS IN EVERY LAYER The degree of diversity in the physical structure of a landscape determines the amount of living diversity that can exist there. Restoration ecologists have known this forever, and they call variation in vegetation structure “habitat heterogeneity.” Many scientists, including Paula Shrewsbury and Michael Raupp in 2000, have shown that, as the vertical and horizontal heterogeneity of a landscape increases, so does the number of species that can make a living within that landscape. Increasing habitat heterogeneity increases the number of niches in a landscape, thus enabling plants and animals to divide the finite resources of a particular place (for example, food, shelter, water, nesting sites, and hunting sites) in ways that minimize competition with each other. This was demonstrated as far back as 1917 by Joseph Grinnell and again by G. Hutchinson in 1957. Competition is fierce in the natural world, and whena new niche appears in a landscape, it does not stay empty very long. This reality long ago inspired the idiom “Nature abhors a vacuum.” Birds illustrate these ecological principles perfectly, as research by Martin Cody in 1974 and by R. MacArthur and colleagues in 1966 shows. Birds can be found using every layer of the landscape, including the subterranean layer if you consider a robin's (or any thrush species) yanking a worm from its tunnel in the soil such a use. Some birds are niche specialists that do nearly everything they need to do within one vegetation layer. Others use several layers over the course of their lives, but are very specific about which layer is used for a particular purpose. A good example of a layer specialist is the ovenbird, a neotropical migrant so named because it makes its nests on the ground out of leaf litter in shapes that resemble little ovens. Not only do ovenbirds nest on the ground, but they also forage for arthropods in ground litter and low-growing groundcovers such as mayapples, foamflower, and ginger. In fact, ovenbirds spend so much time ABOVE A fledgling great horned owl peers from the safety of its perch high in the canopy. It takes a young owl up to three weeks to learn to fly well; during that time fledglings do not stray far from the nest. Parents help feed their young for five months after they leave the nest. LEFT Ovenbirds spend most of their life in the ground layer of forests. They hunt for food, build their nests, and raise their young among the litter on the forest floor. The only time you can see them in the understory is when males perch ona branch and belt out a crescendo of notes to advertise ownership of their territory. Birds in Every Layer 73
ToP Bluebirds, like the great majority of North American birds, rear their young on insects, but they hunt almost exclusively on the ground. This male has just captured a June beetle. Before taking it to his nest, he will search the area for predators to be sure he does not lead any to his young. ABOVE Catbirds build their nests in dense 74 Layers in Wild Landscapes shrubbery and lay 3-5 brilliant blue eggs. Egg color intensity reflects the quality of the mother’s diet: the bluer the eggs, the better the diet. within the ground layer that they have taken on the appearance of chestnut-brown leaf litter to hide from their enemies. The only time ovenbirds leave the ground layer is when males are seeking a mate and delineating their territories. Then they will move to the understory, where they a sing a crescendo of loud notes that seems far too powerful for such a little bird. Other layer specialists include Carolina wrens and yellow-breasted chats (shrub layer); white-breasted nuthatches and all woodpeckers (canopy); rufous-sided towhees and worm-eating warblers (ground layer); and great crested flycatchers and cedar waxwings (understory). Bluebirds (eastern, western, and mountain) are one of many common bird species that hunt for food exclusively in one layer but nest in another. The eastern bluebird, for example, is a tree-hole nester that prefers snags on the edge of, or isolated within, grazed meadows. When it comes time to eat, and particularly to feed their nestlings, bluebirds hunt for insects and spiders on the ground. Bluebirds evolved when ungulate grazers were abundant in North America, even in the well-forested East. They developed a preference for caterpillars, particularly fat cutworm and armyworm larvae that develop on the forbs of well-grazed pastureland, as well as for scarab beetle larvae that feed on grass roots. Free-hunting spiders that frequent the ground layer are also favorites and comprise about 10 percent of their diet. Diet preferences that evolved over many millennia have become hardwired into birds like the bluebird and now dictate where birds forage—or whether they will be in your landscape at all. Many other birds nest in elevated layers of the canopy, understory, or shrubs but forage for food on or near the ground. Catbirds, mockingbirds, and brown thrashers nest in low shrubs or understory trees, but spend a good deal of their time foraging for insects that eat detritus (dead plant parts) on the ground. Perhaps the most beautiful fruit-lover, the cedar waxwing nests on horizontal branches
as high as 50 feet but will seek out fruits from shadbush, elderberry, black cherry, and red cedar in lower landscape layers as soon as those fruits ripen in the summer and fall. Pileated woodpeckers the largest remaining woodpecker species in North America, nest in tree cavities high in the canopy, but because they love to eat carpenter ants, they will forage wherever carpenter ants may be, including within fallen trees on the ground. Even birds we do see commonly, particularly species at our feeders like the Carolina chickadee and tufted titmouse, prefer to nest in canopy tree holes, but ABOVE Although chickadees nest in canopy tree holes, they move to meadows in the fall and winter months to feast on the bounty of seeds this layer offers. In fact, chickadees would not make it through the winter without patches of meadow plants to sustain them. Here a chickadee plucks blackeyed Susan seeds one by one from a flower head. forage for fall and winter seeds in meadows. RIGHT Many common birds including chickadees, titmice, and all woodpeckers nest in canopy tree holes, and they are very specific about the size of the tree hole they will use. If a chickadee chooses a hole too large, it will likely be evicted by a downy woodpecker, red-bellied woodpecker, or evena screech owl. A consistent problem for all tree hole nesters is the shortage of tree holes. 7 I ABOVE Eastern red cedars (Juniperus virginiana) can be common in late-successional habitats where they provide excellent cover for birds as well as copious amounts of nutritious wax-covered cones, often called juniper berries. Juniper berries are favorite winter foods of many bird species, especially cedar waxwings. A single berry will pass through a cedar waxwing's gut in only 12 minutes, but that short internal Lyi treatment improves We) the germination of red *) ie te cedar seeds threefold. Birds in Every Layer 75
Layer specialization by birds is not always static and can change with the seasons. This is usually driven by seasonal changes in diet. The hermit thrush for example, behaves like other thrushes while breeding: it nests in the forest understory but forages for arthropods and worms almost exclusively within the ground layer. Unlike its thrush relatives, however, the hermit thrush does not migrate to the neotropics where insects are abundant all winter. Instead, it remains in the temperate zone, albeit in mid rather than high latitudes, and subsists largely on berries such as those produced by winterberry (/lex verticillata), American holly (Ilex opaca), and flowering dogwood (Cornus florida). These berries can be an abundant and convenient source of food for hermit thrushes, but they are typically claimed and aggressively guarded by another, larger winter berry-eater, the northern 76 Layers in Wild Landscapes lyna
mockingbird. Rather than frequenting the ground layer as they do in the spring and summer, hermit thrushes spend the winter months sitting quietly near such berry sources, darting into a berry shrub for a quick snack whenever the mockingbird on duty turns its back. Although many birds commonly use lower layers in landscapes, the canopy is required at some point in their lives by more birds than any other layer. Moreover, many species like the scarlet tanager, woodthrush, red-eyed vireo, and most warblers are considered interior forest species because they are only comfortable where trees are numerous enough to create a closed canopy. Habitat heterogeneity is not only created by the addition of vertical niches to the landscape; horizontal layers also add much to the structural diversity of habitats. The eastern meadow is a distinct OPPOSITE TOP Poison ivy produces very few caterpillars for birds to eat during the summer, but come fall its white berries provide valuable nutrition for migrating warblers. Herea yellow-rumped warbler prepares to feast. OPPOSITE FAR LEFT Hermit thrushes breed in northern states and Canada but often spend the winter months at mid and southern latitudes in the United States. They forage for arthropods in leaf litter as long as weather permits, but when the ground layer freezes, they rely on berries to sustain them. Here a hermit thrush eyes one of the few remaining on a winterberry (Ilex verticillata). He has to grab it quickly before the resident mockingbird who has claimed the holly for himself chases him off. In the spring and early summer, male yellowthroat warblers sing from bushy scrub for many hours each day to attract females and to warn off competing males. LEFT Scarlet tanagers are residents of mature forests with tall canopies. The difference between males and females is extreme in this bird: males area striking contrast of red and black while females are uniformly tan. ABOVE Although they breed in the boreal forests of Canada, whitethroated sparrows are common winter residents in fields and scrub habitat throughout eastern North America. Like so many other birds, white throats depend on the large seed stocks of unmown meadows to see them through the winter. Birds in Every Layer 77
“) /) } A] 4) ei che} y ve (y fob, =] /) =] o oo , ~ f 4 e £ ay is] 2 ¢ Wy os hes & per) v C3 ry f r WY) head (3) Gc hot & Wy ©. = Fae > Xu a u La XL w 1s) (4 /* [=] =) f (G iy] /) /) & th) i) 4 f f - oO Y & r qd 6 be ri a) a] pf ke WV) rs C W 7] i) (+) a — oN Ww 3 rs god (0 VY) = Ww Wie meg Dy OU atc Mem) tats pro = Sl Ut URS ~ ry gt Cae & POF WAT Ve VEU (G an — — _l2 >"> > >, " ee, Sagowie\§k, a>) ike the UNL’ wet Alec jh tar Ci CUE UES it /) y Of) { ue] s 2s qiyYy (=) s 5m f 4 : Oi “4 J (=) , fale af! = Ws el iy c 7 o oel -~ bh fe fi Vv + 6 0 a =] wv “/) { jd «=Csd 4 Y) oh /) = 4 /) hy "= (0 = & & Ss if 5p L u] 2 Vi WA ve ¢£ s c a] @ ois © i‘ : ts gs . /) (9 Wy ‘hel = rk rd ) i] Vj = Vv) & w rp VY) = & =) (6 i) yn i Fae ts —, 1 CWO Dee nO ES bx TSO em Sm LP nd animal ar a both Oot = ofan mich im = uv Xu . ae > meacow eG A female ruby- and the yellow /. throated hummingbird : A little blue heron waits out a rain Ww VY) “ iy] pallida, are important sources of nectar for hummingbirds, nectars at a jewelweed flower growing along the wet edge. Jewelweed species, both shower at a river's edge. The transitional zone particularly during their September m from North America between water and land is favored by the small 9 V) WY) wy i gration fish, frogs, and insects the orange-flowered that little blues hunt throughout the day. Impat. jens capensis to Central America. 7h) Wy te i
much of their lives in wet edges. Only there is the water shallow enough to provide access to the frogs and fish that are the main food sources of these birds and the vegetation thick enough to provide the cover these birds need when danger approaches. And the willows, birches, and alders that comprise much of the woody vegetation in wet edges are preferred breeding and foraging sites for many smaller birds, such as the beautiful and quite vocal yellow warbler. In fact, the ruby-throated hummingbird will build its nest on a sloping branch over water whenever the opportunity arises. Landscapes with many vegetation layers are landscapes with many birds, because they are landscapes with many plants making many things to eat. Layered landscapes provide a complex of interacting organisms that are both beautiful and fascinating to those who learn to see. More important than their beauty and interest, though, is the fact that layered landscapes are functional landscapes. —DT RIGHT Great egrets industry. They are now are stunning birds that common in marshes and were hunted nearly to pond edges where they extinction at the turn of use their formidable bill to the twentieth century stab small fish and frogs. to support the fashion Birds in Every Layer 79
by combing th € 1and nglish words gland that — st i = recent e powerful than - gh agriculture, industry, f other acti The Cultural Layers 81
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to define any surface that has been written on repeatedly, each time the previous writing having been imperfectly erased and therefore remaining partly legible, Cultural layers are very much like this, They are often easily read when first written, but inevitably become partly masked by successive writings and by environmental processes. The stories inherent in cultural layers can be incorporated in the garden narratives, and insights gleaned from the interactions of culture and ecology can inform the sustainable design and management of gardens. —RD Lert Arailroad once traveled this path. In the near-century since its demise, the forest regrew except in the old bed of cinder ballast. Now part of a preserve, the trail is kept clear partly by crews with saws but largely by human foot traffic. The dark circular vanishing point is the result of shadows in the otherwise sunny early spring landscape, hinting at a turn to the right. In mornings, this trail is full of birdsong. TOP RIGHT Local residents wondering about this grand allée of trees might assume it was planted or follows a watercourse, but it follows the rail bed and is the result of mostly native trees taking advantage of opportunity. The pastures on both sides have been kept clear of trees since the trains stopped running, but once the tracks were removed, the railway was neglected, creating anew linear niche for seedling trees. The community of trees that established along the raiibed 80 years ago is different from what would establish today due to changes in local climate, hydrology, and the presence of naturalized exotic species. riGuT In October, the allée follows the old railway across a local road. The line of trees in the distance follows the course of a creek.
ith along the lroad right of ly summer: el ing sou former ra way in ear oe Ta RL . apie NAR :
This population of wild ginger (Asarum canadense) has been increasing for decades, apparently adapted to current conditions along the shoulder of the cinder bed, just before it slopes down toward the creek. Nodding trillium (Trillium cernuum) is the only trillium species native to this section of the local watershed. Never common, it is diminishing in its traditional niches due to the spread of multiple exotic weeds. For reasons unknown, it is finding new habitat along the shoulder of the railbed. Ants certainly play arole inthis. The pendent flower of nodding trillium in early May. —RD The Cultural Layers 85
ABOVE Relict cultural landscapes can be as beautiful as the best of gardens. The visual order in this scene is the result of vegetation responding to former human activity. This scene at Whitesbog in the New Jersey Pine Barrens was graded more than a century ago by engineers creating 86 Layers in Wild Landscapes conditions suitable for commercial cranberry production. Long abandoned agriculturally, the resulting accidental landscape still reflects this early shaping of the land. OPPOSITE TOP Also created decades ago when the land was engineered for cranberry production, a nearby drainage swale now provides ideal habitat for possumhaw (Viburnum nudum) in the foreground. Highbush blueberries (V. corymbosum) form a self-sown hedge of scarlet along the bank of the swale.
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THE TEMPORAL LAYERS: TIME AND OPPORTUNITY Climate change and the increased presence of nat- _uralizing exotic species have profoundly altered _ the way many modern landscapes regrow after disturbance. This series of photographs charts the regrowth of a section of woods in Pennsylvania's White Clay Creek Preserve following a tornado in July 1994. I'd hiked and botanized in this area for decades and was familiar with the richness of its layering. A variety of oaks, tulip trees, beeches, maples, and hickories formed the canopy. Dogwoods and ironwoods were frequent in the understory. The shrub layer included spicebush, arrowwood viburnum, and mapleleaf viburnum. The herbaceous layer was especially diverse, including white wood asters, wild ginger, multiple ferns and a number of species that are uncommon locally including puttyroot orchid (Aplectrum hyemale), cranefly orchid (Tipularia discolor), and devils’-bit (Chamaelirium luteum). The tornado twisted the tops off more than half of the canopy trees in a wide swath, and many others were broken or toppled. The ground layer was Cleared of decades of accumulated organic matter and much of the soil was laid bare. | knew the preserve had no budget to do much more than clear debris blocking the road and | was curious to see what would evolve in the absence of human intervention. Choosing one distinctive broken tulip tree as a reference point, | began photographing fromthe same approximate position in July 1994. By late October one year later, regrowth was well underway, but it consisted mostly of annual weeds and exotic shrubs and vines including multiflora rose, Japanese honey- ~ suckle, and Oriental bittersweet along with tulip tree seedlings and stump sprouts from beeches. A photo taken approximately five years later in April 2000 shows the exotic growth dominating the lower layers and climbing over the broken tulip tree. | couldn't find any oak or hickory seedlings and only white wood asters and Christmas ferns were still common in the herbaceous layer. Twelve years later in April 2012 the vines and roses had grown to such proportions that | could barely get near the spot I'd originally photographed from in 1994. At one time the most common advice following disturbance was “Let nature take its course,” with the implication that in time everything would return to the way it was. This may once have been appropriate, but it no longer is in many instances. The forest section I've watched is re-vegetating, but with profoundly different structure and composition. The trees felled by the tornado remain on the ground, and as they decompose and release their stored minerals and nutrients, they provide habitat and sustenance for woodland fauna. This is desirable. However, if the desire is also for the woods to regenerate some semblance of its former diversity, human intervention is essential—but at what cost? lf one were to start with the landscape in 2012, huge effort would be required just to clear the exotic woody growth. Since many of the native species that would once have dispersed seeds are no longer present, deliberate planting would be necessary. Imagine beginning the same task in 2000 and it would require less effort. Beginning in 1995 would have been even easier. The best opportunity presented itself in 1994. Embarking on a program to watch the ground and remove weed seedlings so that indigenous species could re-establish was then a relatively low-cost option. Continuing this over the years would have provided a more desirable outcome at a fraction of the total resource cost. Parks and preserves may not have the staffing to do this, but it is a realistic option for residential landscapes. The amount of discretionary time two stereotypically busy people can devote on a per-acre basis to taking care of their home garden greatly exceeds the staffing of most parks. The key is to be watchful and intervene efficiently in response to opportunity. —RD The Temporal Layers: Time and Opportunity 91
WHAT DO WE MEAN BY NATIVE®: Life would be simpler if we could discuss the complex relationships between plants, animals, place, and time without relying on the word native, but this isn’t likely to be the case anytime soon. Typically poorly defined or undefined, native often confuses more than it clarifies. Definitions, when provided, sometimes rely on geographic or political boundaries such as “naturally occurring within 200 miles” or “naturally occurring in Pennsylvania.” These definitions fail to connect organisms to ecosystems, which rarely coincide with arbitrary boundaries. Another prevailing approach relies on human influence as a deciding criterion such as “occurring in a given geographic area without human involvement” or “occurring within the state boundaries prior to European contact.” These definitions perpetuate the ideological separation of humans from all other organisms, a concept soundly rejected by modern ecological science. If the term is to have clear relevance now and in the future, it requires a definition recognizing that native status accrues from origin, evolution, and functionality. What is native in any given place today wasn’t native if we look back far enough in time, and it is certain that what will be native in that same place in the future will be different from what is native now. Functional ecological relationships take a long time to evolve—often thousands of years—but they do evolve. Humanity’s challenge is to reduce its introduction of rapid environmental changes that are currently causing extinctions to occur faster than the evolution of new species. With all the above in mind, for the purpose of this book and future discussion we've created the following definition: The tiny blue dot (circled) is a great blue heron witha 5-foot wingspan flying 50 feet above the surface of the White Clay Creek, photographed froma helicopter flying 300 feet above this intricately layered Pennsylvania landscape. native: a plant or animal that has evolved ina given place over a period of time sufficient to develop complex and essential relationships with the physical environment and other organisms ina given ecological community.
CHAPTER TWO The Community of Living Organisms: Why Interrelationships Matter More Than Numbers by Doug Tallamy THE PROMINENCE OF SPECIALIZEI In the mountain cloud forests of Central America a brilliant green-and-red bird with tail feathers twice the length of its body sits motionless among the epiphytes growing on a branch some 120 feet off the ground. After several minutes, it darts through the air to a nearby tree limb, plucks an inch-long fruit off the branch, and returns to its perch. Once settled, the bird swallows the fruit whole . .. and sits. Perhaps 20 minutes later, the bird regurgitates the large pit of the fruit and the process starts again. Birders worldwide recognize this as a description of the resplendent quetzal pursuing its favorite food, fruits of the wild avocado tree (Persea americana), the progenitor of our cultivated avocados. To characterize avocados as a favorite food of quetzals is an understatement, because at this point in its evolutionary history, avocados are essential to the quetzal’s existence. Although they also eat insects, frogs, and lizards, as well as fruits from other plants inthe — Lauraceae, quetzals have grown so dependent on the rich fats and proteins provided by avocado fruits that they can no longer live where there are no avocado trees. When the forests of Central America were intact, this degree of diet specialization was not a problem for quetzals. 94
Today, however, with wild avocados themselves threatened, dependence on avocado fruits has placed quetzals firmly on the road to extinction. For those interested in quetzal conservation, the solution to their dwindling numbers is obvious; plant avocado trees! The same can be said of other tropical creatures with specialized diets. To save the great green macaw, plant the mountain almond (Dipteryx panamensis) as fast as possible. To sustain populations of jaguars, save the palm trees that make the palm nuts that support large peccary populations, the wild pigs that are required components of jaguar diets. To be sure, highly specific relationships between food and consumer are more common in tropical ecosystems, but some level of diet specialization is easily found in temperate zones as well. In fact, one or more species of the bolas spider, one of the most specialized predators in the world, can be found in residential landscapes throughout much of the United States. Rather than spin an intricate web, adult female bolas spiders use a single strand of silk tipped with a bolas of sticky goo. They then hang off the end of a leaf, patiently holding their line as if they were fishing. The chances that an insect will fly into the sticky bolas by accident seem infinitely small, yet often within minutes a moth flies directly to the bolas and becomes entangled. How can this happen? It can happen through extraordinary chemical mimicry. Over the eons, bolas spiders developed the ability to manufacture the female sex pheromone of a particular species of moth. A hunting bolas spider appears to be waiting passively for a moth to fly to its bolas, but, in reality, it is releasing copious amounts of the moth’s sex pheromone, a chemical that can attract male moths of the appropriate species from hundreds of yards away. Each species of bolas spider has mimicked the pheromone of a single moth species, forming a unique relationship between predator and prey. LEFT A pipevine swallowtail lays eggs on Aristolochia macrophylla in mid-June. ABOVE Resplendent quetzals depend on the fats and protein in wild avocado fruits during much of the year. The Prominence of Specialized Relationships 95
The bolas spider (Mastophora phynosoma) mimics the sex pheromone of asingle species of moth to attract them to its sticky bolas. Most people are unaware of the bolas spiders hunting in their yard, even though this isa common occurrence. A specialized relationship that many have observed involves the Carolina chickadee. If asked what chickadees eat, most people would confidently answer “seeds.” Their confidence would be borne out of personal experience. Chickadees are one of the most common customers at our backyard birdfeeders and they do indeed spend the winter months eating a variety of seeds. When it comes time to reproduce, however, chickadees become diet specialists. Like 96 percent of the terrestrial birds in North America, Carolina chickadees rear their young on insects. And not just any old insect; they feed nestlings caterpillars, the larvae of moths, butterflies, and sawflies. Chickadee parents could feed their young crickets, millipedes, sow bugs, crane flies, katydids, treehoppers, click beetles, spiders, cockroaches, horse flies, or bumblebees, but 95-100 percent of the insects they hunt for their offspring are caterpillars. 96 The Community of Living Organisms Because chickadees rear their young exclusively on caterpillars, there will be no chickadees where there are no caterpillars. We really should say that there will be no chickadees where there are not enough caterpillars to bring a clutch of eggs to independence from parental care. An environment that produces almost enough caterpillars just won't do. How many caterpillars are enough to produce a clutch of chickadees? 75? 150? Not quite. Carolina chickadees bring somewhere between 390 and 570 caterpillars to their nest each day, depending on how many chicks are in the nest. Parents feed nestlings in the nest for 16 to 18 days before the young fledge, and then for several more days after fledging. If we focus only on the caterpillars required to reach fledging, it takes 6,240 to 10,260 caterpillars to fledge a single clutch of chickadees, an astounding number, even to those who study bird behavior. What’s more, chickadees are tiny birds; a Carolina chickadee weighs a third of an ounce, the equivalent of four pennies. In comparison, a red-bellied woodpecker, which also rears its young on insect larvae, weighs eight times more than a chickadee. How much insect biomass is required to create a red-bellied woodpecker? How many insects are required to sustain an entire population of chickadees and woodpeckers... and titmice, and orioles, bluebirds, woodthrushes, robins, and all of the other birds that signal healthy temperate zone ecosystems? The numbers are mind-boggling. Before we consider what types of landscapes are capable of producing such large numbers of insects, we have to consider another type of relationship: the relationship between the insects that eat plants and the plants they eat. Most insect herbivores, some 90 percent in fact, are diet specialists. Just like breeding Carolina chickadees, they are restricted to eating very specific types of plant food.